EP1914388A1 - Sealing element for sealing a leakage passage between a rotor and a stator of a turbomachine. - Google Patents

Abstract

The seal (34) has a bending body (42), which changes its form based on its temperature, where a bending body is formed of a bi-metal, and the bending body is provided with brushing hairs. The bending body is highly bent or kinked in temperature of the bending body, which corresponds to a idleness of a turbo machine, than in temperature, which corresponds to a full load operation of the associated turbo machine. An independent claim is also included for a thermal turbo machine with a rotor and a stator.

Description

The invention relates to a sealing element for sealing a leakage gap through which a flow medium can flow between a rotor and a stator of a thermal turbomachine. The invention further relates to a thermal turbomachine, in particular a gas turbine or steam turbine, which is provided with such a sealing element.

Thermal turbomachines such as steam or gas turbines usually have a rotatably mounted in a fixed housing rotor. The fixed machine assembly of a thermal turbomachine is also referred to as a stator. Between the rotor and the stator extends in the axial direction of a flow channel, in which protrude a number of combined into groups of blades or rows of blades blades. The kinetic energy of the working medium flowing through the flow channel is transmitted to the rotor shaft by impulse transmission via the rotor blades. The rotational energy thus generated can, for. B. be used to drive an electric generator.

In a gas turbine usually the turbine unit is preceded by a compressor unit. The blades of the turbine unit and the compressor unit are preferably arranged on a common rotor shaft. The compressor draws in cold ambient air, compresses it and then feeds it to a combustion chamber, where it is first mixed with a fuel and then burned. The resulting gases flow at high speed into the flow channel of the turbine unit and drive their rotor. The mechanical energy generated in this way is partly fed back to the thermal turbomachine and used to drive the compressor.

A thermal turbomachine may have guide vanes mounted on the stator and projecting into the flow channel and upstream of the rotor blades. The guide vanes are usually also combined to blade rows or blade groups. The task of the guide vanes is a suitable for the operation of the turbine beam guidance between successive blade rows. In general, the guide blade rows and the rotor blade rows are arranged alternately. A successive unit of a row of vanes and a blade row is also referred to as a turbine stage in a turbine and as a compressor stage in a compressor.

The efficiency of a thermal turbomachine is among other things influenced by the gap located between the rotor and the stator. This gap, which is as small as possible, is also called a leakage gap. The leakage current flowing in the leakage gap and deviating from the intended flow path occurs, for example, equally between the rotor shaft and the surrounding housing and between the rotor blades or guide vanes and the housing in the turbine and the compressor. In order to keep the resulting power losses as low as possible, suitable seals between the stationary and rotating assemblies of the thermal fluid machine are used.

One type of seal commonly used in gas or steam turbines is the labyrinth seal. Such a seal is relatively simple and works at least in principle without significant wear over long periods of operation. In this case, sealing lips or sealing rings which are installed in one or more components of the stationary and / or rotating turbine part and are projecting into the leakage gap are arranged in the manner of annular diaphragms, whose throttling effect causes a reduction of the leakage current. By the series connection of several profile panels, possibly by a stepped or toothed version In the labyrinths, the leakage current can be further reduced. Because of the relatively large radial and axial movements of the shaft and the housing but comparatively large residual gaps are still required, so that the efficiency of the turbomachine limiting leakage current is still quite large.

In order to keep the gaps as small as possible, it is occasionally permitted to cut the sealing strips into a wear-resistant counter-ring. This may for example consist of a nickel-graphite alloy or a metallic or ceramic honeycomb structure. Such constructions work satisfactorily when temporary thermal expansion differences occur between the rotor and the stator. In modern high-performance turbomachinery, however, there are not only the temporally different thermal expansion of the components but also considerable radial deflections due to high radial acceleration of the rotor and thrust-induced bending of the housing. If the sealing strips cut very deeply into the counter rings, this leads to a deterioration of the sealing behavior. In addition, such Anstreifvorgänge always the risk of major machine damage when z. B. detach larger fragments of the sealing rings and are thrown at high speed against the components of the subsequent turbine stages or due to thermal distortion.

Another alternative seal is the bristle rim brush seal. Such a seal may be composed of one or more bristle packages, wherein the bristles of the respective bristle pack are anchored directly in a rotor component or stator component delimiting the leakage gap or leakage channel. The fixed to the respective turbine component bristles bridge the distance between the fixed and the rotating component, wherein the bristles with their free end at least during operation of the turbomachine at the opposite lying turbine component can grind. This creates a seal with only small leakage currents. Due to the elasticity of the bristles a radial movement of the two components against each other is possible to a certain extent with a relatively constant tightness. An arrangement of the bristles inclined up to 45 ° to the direction of rotation reduces the risk of buckling, reduces the frictional torque and causes the brushes to close when they are pressurized. A significant advantage of bristle seals is also their low installation space requirement. As a result, a turbomachine, in particular a gas or steam turbine, can be made extremely compact, which reduces the material requirement.

However, the bristle seals have the significant disadvantage that only limited relative radial movements between the components can be compensated. Namely, the relative movements are too large, there is a risk of damage and a subsequent loss of sealing effect. This is significant because damage to the bristle seal, the sealing effect can be almost completely lost. The freely movable sections of the bristles can not be run arbitrarily long. In view of the compressive strength of the bristle seal and to avoid caused by the flow pressure of the flow medium "fluttering" of the bristles, the height of the gap between the intended for receiving the bristles metal frame and the opposite turbine component is listed as small as possible. Contact of such a socket or receptacle for the bristles, which often also includes a projecting into the leakage space support wall for the bristles, with the opposite turbine component must be avoided in any case, to greater damage to the surrounding components or in the extreme case of the entire turbine unit prevent. It would be desirable to avoid the above-mentioned problems in the sealing of the leakage gap and to specify a sealing system, which in all operating conditions of the turbomachine at high durability ensures good tightness. The gasket should be tolerant of gap width variations by being able to cover different widths.

The invention is therefore an object of the invention to provide a sealing element of the type mentioned above, which effectively seals the leakage gap between the rotor component and the stator in each operating condition of the turbomachine, which also temporarily occurring relatively large gaps between the components should be compensated without loss of tightness.

This object is achieved according to the invention in that the sealing element has a bending body which changes its shape as a function of its temperature.

The invention is based on the consideration that the leakage gap change between the rotor component and the stator component of a thermal turbomachine, in particular a gas and steam turbine, can be sealed particularly effectively by a temperature-sensitive sealing element. This makes sense, since the radial relative movements of the components during different operating phases of the turbomachine in addition to different centrifugal force and shear-induced strains and shifts is ultimately dependent on the thermal expansion processes. By such a sealing concept, the efficiency, which increases with decreasing leakage flow, would be significantly improved in the control mode of the turbomachine. It should therefore be sought to use a temperature-controlled sealing element, so on the one hand a required large cold play between the rotor component and the stator component is ensured and on the other hand, the leakage gap is kept as small as possible in normal operation.

It is therefore desirable to use a sealing system which, depending on the temperature in the leakage gap between the rotor component and the stator component changes its shape in such a way that in each operating state only a minimal residual gap permeable by the flow medium remains. For this purpose, the sealing element has a bending body which bends more or less as a function of its temperature. In this case, the bending body is connected at one end to the rotor component and / or the stator component. A system created in this way also compensates for large changes in the gap geometry.

To ensure a particularly high density of the bending body is provided with a preferably attached to the free end of the bending body additional sealing element in a particularly advantageous embodiment. In a sealing system designed in this way, the bending body acts as an actuator, whereby the additionally attached sealing element can be positioned with regard to an effective sealing of the leakage gap. Thus, sealing concepts can be realized, which have not worked at all or only unsatisfactory at relatively large leakage gaps. Also conceivable is such a sealing system with a lever device which is connected between the additionally mounted sealing element and the bending body acting as an actuator. In particular, so that, for example, a larger travel distance can be achieved, whereby too small deflections of the bending body can be compensated.

The required for the availability and reliability of the turbomachine gap between the rotor component and the stator in the stationary state of the turbomachine and during the start-up process is adjusted by the fact that the bending body is preferably more curved at standstill of the turbomachine than in rated load operation. Thus, a sufficiently large "cold play" between the rotor component and the stator component can be kept. The no longer required in nominal load operation "cold play" is minimized by a less bent in this operating condition of the turbomachine bending body.

The bending body of the sealing element is preferably formed from a bimetal, which consists of two mutually positively or cohesively connected metal layers. Due to the unequal coefficients of thermal expansion of the interconnected metals, these expand to a different extent as the ambient temperature is increased, in this case as the temperature in the leakage gap increases. As a result, the bending body bends according to its temperature. Conversely, the degree of bending of the bending body decreases again when the ambient temperature and thus also the bimetal cools again. The sealing element thus adapts continuously to the temperature of the working medium and the structure surrounding the sealing element.

In an alternative or additional advantageous development of the bending body may also be formed of a memory metal, which is also known as shape memory alloy. This metal is characterized by the property of "creative memory," which can be triggered either thermally or mechanically. Even after a severe deformation, this material is able to resume a previously "embossed" shape. In contrast to the bimetal, the change in shape occurs relatively abruptly at a certain temperature, which depends on the material. The timing of this change in shape of a bending body thus formed can be adjusted by selecting suitable alloys. This is as well as the use of a bimetal of the gap size adapted shape of the bending body possible.

The change in shape of the memory metal is advantageously subject to a two-way memory effect. This ensures that a change in shape occurs both at a temperature increase and during a cooling of the bending body, without an external load is required, whereby in a bending body formed from such a material, the provision must therefore not be done manually. The change in shape between two different shapes is thus without renewed mechanically induced shape change repeatable (intrinsic two-way effect).

In a further advantageous embodiment of the bending body is provided with protruding from him bristle hairs. This combination allows a particularly effective sealing of the leakage gap between the rotor component and the stator component. Compared with already known bristle seals, the bristles can be kept rather short, since in an operating state with maximum size of the leakage gap, the bristles due to the effective as an actuator bending body does not have to fill it completely. A seal without such a temperature-controlled dynamic adaptation to the gap changes by the bending body would have the consequence that especially during the start-up of the turbomachine, the bristles are heavily stressed because of their length and thus there is a high risk of buckling.

The sealing system described can advantageously be used at different locations between fixed and moving, in particular between fixed and rotating parts or assemblies. However, particularly preferred is the use of temperature-sensitive sealing elements for sealing the leakage gap occurring between the rotor and the stator of a thermal turbomachine, in particular a gas or steam turbine.

The advantages achieved by the invention are, in particular, that the leakage gap can be dynamically sealed by the use of sealing elements, which have an ambient temperature adapting shape. Because the size of the leakage gap is based essentially on a different thermal expansion of the rotor and stator of a thermal fluid machine, such a sealing system for gap sealing is particularly suitable. In particular, in the execution of a classic labyrinth seal thus creates an extremely low-wear system, which also has an excellent sealing effect.

FIG 1

eine schematische Darstellung einer Dampfturbine im Längsschnitt, und

FIG 2 bis 8

jeweils eine Dichtungsanordnung mit einer Anzahl von Dichtelementen.

An embodiment of the invention will be explained in more detail with reference to a drawing. Show:

FIG. 1

a schematic representation of a steam turbine in longitudinal section, and

FIGS. 2 to 8

each a seal assembly with a number of sealing elements.

Identical parts are provided with the same reference numerals in all figures.

1 shows a longitudinal section through a steam turbine 2 as an example of a thermal turbomachine. The steam turbine 2 has a number of rotatable blades 6 connected to the turbine shaft 4. The blades 6 are each arranged in a ring shape on the turbine shaft 4 and thus form a number of blade rings or blade rows. Furthermore, the steam turbine 2 comprises a number of fixed guide vanes 8, which are likewise fixed in a ring shape to form turbine blade rings or rows of vanes on a turbine housing 10 of the steam turbine 2. Deviating from the illustration in FIG. 1, the guide vanes 8 can also be fastened to an inner housing arranged inside the outer turbine housing 10 or to guide blade carriers.

The limited by the turbine shaft 4 and the turbine housing 10 flow channel 12, which is also referred to as expansion section, the input side is acted upon by an annular inflow opening 14 with standing under high pressure and high temperature steam D. The steam D flows through the flow channel 12 in a direction parallel to the central axis 16 of the steam turbine 2 extending main flow direction, where it relaxes work and thereby drives the turbine shaft 4 by impulse transmission to the blades 6.

The guide vanes 8 serve to guide the flow of the steam D, which is provided as the working medium, between in each case two rows of blades viewed successively in the direction of flow. A successive pair of a ring of vanes 8 or a row of vanes and a ring of blades 6 or a blade row is also referred to as a turbine stage. The relaxed after flowing through the expansion section steam D accumulates in an end arranged in the steam turbine 2 outlet region 18 and is discharged via a line not shown here from the turbine housing 10.

The pressure gradient across the blades causes a thrust in the direction of flow. This thrust is compensated by a thrust balance piston 20, which is also acted upon on the side facing away from the flow channel 12 with pressurized steam D, to a defined residual thrust. The entirety of the fixed turbine parts, that is to say the turbine housing 10 together with the guide vanes 8, is also referred to as stator 21. The rotating parts, so the turbine shaft 4 with the blades 6, are referred to in their entirety as a turbine rotor or rotor 22.

To realize a high efficiency, the leakage currents of the steam D occurring at various points between the rotor 22 and the stator 21 of the steam turbine 2 should be minimized. Such leakage flows occur, for example, within the annular leakage gaps 26 between the turbine shaft 4 and the respective edge portion of the turbine housing 10 positioned in the axial direction in the axial direction, whereby vapor D escapes into the environment. Also undesirable is an overflow of the steam D within the lying between the thrust balance piston 20 and the turbine housing 10 leakage gap 27. Finally, there are also leakage gaps 28, 29 between the blades 6 a blade row associated blade cover 24 and the surrounding turbine housing 10 and between a the guide vanes eighth a Leitschaufelreihe associated Leitschaufeldeckband 24 and the opposite section of the rotor 22.

In order to minimize the leakage losses, the steam turbine 2 has a number of shaft seals 30 for sealing the leakage gaps 26 between the turbine shaft 4 and the turbine housing 10 and a thrust balance piston seal 32 for sealing the leakage gap 27 between the thrust balance piston 20 and the turbine housing 10 , Furthermore, sealing elements 34 are provided for sealing the leakage gaps 28, 30 between the respective guide blade cover strip and the rotor 22 or between the respective blade cover strip and the turbine housing 10. The seals 30, 32, 34 between the rotor 22 and the stator 21 of the steam turbine 2 are indicated only schematically in FIG. 1 and will be explained in more detail below.

The sealing arrangements 36 shown in detail in FIGS. 2 to 8 each show a sealing system between the rotor 22 and the stator 21 of the steam turbine 2, which may be a shaft seal 30, a thrust balance piston seal 32 or a turbine blade seal 34. The seal assembly 36 is anchored to a seal carrier element 38, 40 of a turbine component. For the following discussion, it is assumed that the turbine component is a rotor component 38 and a stator component 40.

The sealing elements 32 comprising a sealing body 42 shown in FIGS. 2 to 8 are connected at one end to the rotor component 38 or the stator component 40 of the steam turbine 2, while the free end projects into the leakage gap 26.

FIGS. 2A and 3A show bending bodies 42 bent in the flow direction 44 at an ambient temperature corresponding to the stoppage of the steam turbine 2. The between the free end of the bending body 42 and the stator 40th Occurring residual gap 46 is necessary to compensate for the different thermal expansion between the rotor 22 and the stator 21. This residual gap 46 should be sufficiently large for the starting process of the steam turbine 2, so that the rotor 22, which reaches the operating temperature faster than the turbine housing 10 of the steam turbine 2, does not collide with the turbine housing 10. By the degree of bending of the bending body 42, the residual gap 46 can be preset according to the operational gap change between the rotor 22 and the stator 21.

After reaching the operating temperature of the steam turbine in rated load operation of the bending body 42 takes due to the temperature increase in the leakage gap 26 as shown in Figures 2B and 3B straight shape, whereby a high sealing effect is achieved by the relatively small residual gap 46.

A bending body 42 formed from a memory metal is shown in FIGS. 2A and 2B, wherein the bending body is connected at one end to the rotor component 38.
2A shows a bending body projecting into the leakage gap 26, strongly bent at a location of the memory metal, and FIG. 2B shows a bending body 42 with a straight shape that projects into the leakage gap 26 with its free end.

In order to ensure dynamic adaptation of the bending body 42 to the leakage gap 26 when the mode of operation of the steam turbine 2 changes, the bending body 42 formed from a memory metal is subject to a two-way effect. That is, a defined change in shape of the bending body 42 occurs both during its heating and during its cooling.

Analogous to FIGS. 2A and 2B, FIGS. 3A and 3B show a bending body which is connected to the rotor 38 in a material and / or form-locking manner. On the other hand, this bending element 42, which acts as a sealing element 34, is made of a bimetal formed, which changes its shape continuously with a temperature change of the bending body 42, in contrast to a bending body formed of a memory metal.

The indicated in Figure 4 Leckagespaltabdichtung is designed as a labyrinth seal and comprises three in the flow direction 44 of the working medium of the steam turbine 2 successively arranged from a memory metal formed bending body 42, wherein the degree of bending of the sealing elements 34 seen opposite to the flow direction 44 increases. In this case, the sealing elements 34 are bent unequally strongly in accordance with a temperature profile in the leakage gap 26 or correspondingly differently adjusted deformation temperature. The temperature profile shown in this figure corresponds to a continuous increase in temperature in the flow direction 44 of the working medium of the steam turbine 2.

A sealing arrangement 36 with three sealing elements 34 arranged in succession on the stator component 40 in the flow direction 44 is shown in FIG. Each of the bending bodies 42 is formed from a bimetal, wherein the bending body 42 arranged centrally in the flow direction projects with its free end into a recess 48 introduced through a rotor component 38 and extending in the periphery of the rotor.

FIG. 6 shows three bending bodies 42 acting successively on the stator component 40 in the flow direction 44 as effective sealing elements 34, wherein each bending body 42 is bent counter to the flow direction 44.

A seal arrangement 36 in the embodiment of a labyrinth seal in which the bending bodies 42 acting as sealing elements 34 are arranged alternately one behind the other on the stator component 40 and on the rotor component 38 as seen in the flow direction 44 is shown in FIG. In this case, the bending bodies have a shape bent counter to the flow direction 44.

8 shows a multiply bent bending body 42 consisting of a memory metal, for example a NiTi, CuZn or FeNiAl alloy, at the free end of which bristles 50 are attached to improve the sealing effect. By such a geometry of the bending body 42 and thus a comparatively large dimension of the bimetal, the thermodynamic efficiency increases significantly compared to the sealing elements 34 shown in the preceding figures. Another essential advantage of this seal arrangement is the combination of a bristle seal with the bending body 42 according to the invention, which is effective as an actor. In this case, the bending body 42 is connected at one end to the rotor 38 positively and / or non-positively. From the free end of the bending body 42 are projecting into the leakage gap bristles 50 from. The controller, d. H. the opening and closing of the seal is in such a seal arrangement in interaction with the temperature difference occurring in the leakage gap. Thus, the leakage current depends on the respective sealing position. The sealing system created in this way has very good sealing properties even with large changes in the gap width 26.

In the embodiment, the operation of the respective sealing element is explained with reference to a steam turbine. Of course, such sealing elements can also be used in other suitable systems or thermal turbomachines, preferably in stationary gas turbines.

Claims (8)

Sealing element (34) for sealing a leakage gap (26, 27, 28, 29) through which a flow medium can flow between a rotor (22) and a stator (21) of a thermal turbomachine,
which has a bending body (42) which changes its shape as a function of its temperature. Sealing element (34) according to claim 1,
whose bending body (42) is effective as an actuator for a different from him and with respect to its sealing effect adjustable sealing element (34). Sealing element (34) according to claim 1,
whose bending body (42) is more bent or kinked at a temperature of the bending body (42) corresponding to the standstill of the turbomachine than at a temperature of the bending body (42) corresponding to the rated load operation of the associated turbomachine. Sealing element (34) according to one of claims 1 to 3, whose bending body (42) is formed of a bimetal. Sealing element (34) according to one of claims 1 to 4, whose bending body (42) is formed of a memory metal. Sealing element (34) according to claim 5,
wherein the shape change of the memory metal is subject to a two-way memory effect. Sealing element (34) according to one of claims 1 to 6,
wherein the bending body (42) is provided with brush hairs (50) protruding therefrom. Thermal Turbomachine,
in particular gas turbine or steam turbine (2),
with a rotor (22) and with a stator (21),
in which a leakage gap (26, 27, 28, 29) located between the rotor (22) and the stator (21) and permeable by a flow medium is sealed with at least one sealing element (34) according to one of claims 1 to 7.

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